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| United States Patent |
5,525,670
|
|
Nishi
, et al.
|
June 11, 1996
|
Aqueous coating composition and coating process using the same
Abstract
The present invention provides the improvement of coating workability (e.g.
pinhole resistance, sagging resistance, etc.) of an aqueous coating
composition. That is, the present invention provides an aqueous coating
composition which comprises: (A) an acrylic resin and/or a polyester resin
having an acid value of 10 to 100, a hydroxyl value of 20 to 300 and a
number average-molecular weight of 1,000 to 50,000; (B) a polycarbonate
resin having a number average-molecular weight of 1,000 to 10,000 which
contains a hydroxyl group at the terminal end; and (C) a curing agent.
| Inventors:
|
Nishi; Tadahiko (Yamatokoriyama, JP);
Ogawa; Hideaki (Hirakata, JP);
Tanabe; Hisaki (Yawata, JP);
Takeuchi; Kunihiko (Mino, JP)
|
| Assignee:
|
Nippon Paint Co., Ltd. (Osaka, JP)
|
| Appl. No.:
|
287902 |
| Filed:
|
August 9, 1994 |
Foreign Application Priority Data
| Aug 10, 1993[JP] | 5-198329 |
| Apr 28, 1994[JP] | 6-091796 |
| Current U.S. Class: |
524/512; 524/513; 524/522; 524/537; 525/124; 525/125; 525/131; 525/155; 525/159; 525/162; 525/185; 525/439 |
| Intern'l Class: |
C09D 167/02; C09D 167/08; C09D 169/00; C09D 133/00 |
| Field of Search: |
524/512,513,522,537
525/124,125,131,155,159,162,185,439
|
References Cited
U.S. Patent Documents
| 5030683 | Jul., 1991 | Nakamura | 524/512.
|
| Foreign Patent Documents |
| 0458243 | Nov., 1991 | EP.
| |
| 0554865 | Aug., 1993 | EP.
| |
| 562577 | Sep., 1993 | EP.
| |
| 009434 | Jan., 1993 | JP.
| |
| WO92/1132 | Jul., 1992 | WO.
| |
Primary Examiner: Buttner; David
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Claims
What is claimed is:
1. An aqueous coating composition which comprises:
(A) a polyester resin having an acid value of 10 to 100, a hydroxyl value
of 20 to 300 and a number average-molecular weight of 1,000 to 50,000,
said polyester resin being an oil-free polyester resin obtain by
condensing a polyhydric alcohol with a polyhydric carboxylic acid, or an
alkyd resin obtained by condensing a polyhydric alcohol and a polyhydric
carboxylic acid with a coconut oil, a castor oil, a dehydrated castor oil,
a linseed oil, a tall oil, a safflower soil, a soybean oil or a fatty acid
thereof;
(B) a polycarbonate resin having a number average-molecular weight of 1,000
to 10,000, which contains a hydroxyl group at the terminal end; and
(C) a curing agent.
2. An aqueous coating composition which comprises:
(A) an acrylic resin and/or a polyester resin having an acid value of 10 to
100, a hydroxyl value of 20 to 300 and a number average-molecular weight
of 1,000 to 50,000;
(B) a polycarbonate resin having a number average-molecular weight of 1,000
to 10,000, which contains a hydroxyl group at the terminal end;
(C) a curing agent; and
(D) acrylic resin particles having a particle size of 0.01 to 1.0 .mu.m.
3. The aqueous coating composition according to claim 1, wherein the
polyester resin of the component (A) is an oil-free polyester resin
obtained by condensing a polyhydric alcohol with a polyhydric carboxylic
acid, or an alkyd resin obtained by condensing a polyhydric alcohol and a
polyhydric carboxylic acid with a coconut oil, a castor oil, a dehydrated
castor oil, a linseed oil, a tall oil, a safflower oil, a soybean oil or a
fatty acid thereof.
4. The aqueous coating composition according to claim 1, wherein the
polycarbonate resin of the component (B) is a resin obtained by reacting a
carbonate monomer selected from a dialkyl carbonate and an alkylene
carbonate, with a straight-chain dihydric alcohol, a branched-chain
dihydric alcohol and a polyhydric alcohol having three or more hydroxyl
groups, wherein the amount of the branched-chain dihydric alcohol is at
least 10 molar % based on the total amount of the alcohol and the amount
of the polyhydric alcohol having three or more hydroxyl groups is not less
than 10 molar %.
5. The aqueous coating composition according to claim 1 or 2, wherein the
curing agent of the component (C) is a melamine resin.
6. The aqueous coating composition according to claim 1 or 2, wherein the
curing agent of the component (C) is a blocked polyisocyanate.
7. The aqueous coating composition according to claim 1 or 2, wherein the
amount of the component (A) is 35 to 70% by weight, the amount of the
component (B) is 5 to 50% by weight and the amount of the component (C) is
10 to 40% by weight; % by weight being based on the weight of the solid
content of the composition.
8. The aqueous coating composition according to claim 1, which further
comprises acrylic resin particles (D) having a particle size of 0.01 to
1.0 .mu.m.
9. The aqueous coating composition according to claim 8 or 2, wherein said
acrylic resin particles have an acid value of 5 or more, which contain a
carboxyl group.
10. The aqueous coating composition according to claim 8 or 2, wherein said
acrylic resin particles are three-dimensionally crosslinked.
11. The aqueous coating composition according to claim 9, wherein said
acrylic resin particles are not three-dimensionally crosslinked.
12. The aqueous coating composition according to claim 8 or 2, wherein the
amount of the component (D) is 3 to 70 parts by weight, based on 100 parts
by weight of the total weight of the solid content of the components (A)
to (C).
13. The aqueous coating composition according to claim 1 or 2, which
further comprises a metal pigment in the amount of 2 to 100 parts by
weight, based on 100 parts by weight of the resin solid content of the
aqueous coating composition.
14. An aqueous coating composition which comprises:
(A) an acrylic resin and/or a polyester resin having an acid value of 10 to
100, a hydroxyl value of 20 to 300 and a number average-molecular weight
of 1,000 to 50,000;
(B) a polycarbonate resin having a number average-molecular weight of 1,000
to 10,000, which contains a hydroxyl group at the terminal end; and
(C) a curing agent;
(D) acrylic resin particles having a particle size of 0.01 to 1.0 .mu.m,
and
(E) a metal pigment.
15. The aqueous coating composition according to claim 14, wherein said
acrylic resin particles (D) have an acid value of 5 or more, which contain
a carboxyl group.
Description
FIELD OF THE INVENTION
The present invention relates to an aqueous coating composition providing a
coat having good appearance, which is superior in coating workability
(e.g. pinhole resistance, sagging resistance, etc.) and surface
smoothness.
BACKGROUND OF THE INVENTION
Aqueous coating compositions are used for intercoating and base topcoating
of automobiles. Heretofore, organic solvent type coatings have been
exclusively used for automobiles. However, it is now strongly demanded to
change from organic solvent type coatings to aqueous coatings in view of
safety on coating process, reduction of environmental pollution,
resources-saving and the like.
As the aqueous intercoating composition, for example, there have been known
an aqueous intercoating composition comprising a carboxylic
group-containing resin, an urethane bond-containing diol and resin
particles (Japanese Patent Laid-Open Publication No. 3-52973), a
thermosetting aqueous coating composition comprising a polyhydric
carboxylic acid resin, an amino resin, a linear low molecular weight
polyester diol and an benzoin (Japanese Laid-Open Patent Publication No.
4-93374) and the like. However, various problems are arisen when using
them for intercoating.
That is, surface smoothness and final appearance are not sufficient.
Further, "pinhole" as a defective appearance caused by bumping of water
during curing a coated film is liable to be arisen in comparison with a
conventional organic solvent type paint. This phenomenon is observed in
case that the film thickness is 20 to 40 .mu.m and it becomes the cause of
deterioration of the final appearance. Further, water resistance of the
coating containing the linear low molecular weight polyester diol is not
sufficient.
In general, a two coat/one bake coating process which comprises coating a
metallic base paint containing a metallic pigment on a plate on which
primer-coated and intercoated (referred to as topcoating), followed by
wet-on-wet coating a clear paint without curing the metallic base coat,
and then simultaneously curing the metallic base coating and clear
coating, is used for coating automobiles. In the metallic base paint used
for this process, a flake metal pigment (e.g. aluminum) is satisfactorily
oriented so that an excellent appearance of the coated film can be
obtained.
Particularly, an aqueous metallic base coating composition comprising a
water dispersant of an amide group-containing acidic resin and hydrophilic
group-carrying polyurethane resin as a main component (Japanese Laid-Open
Patent Publication No. 4-25582) is known as to the above application.
However, "pinhole" as a defective appearance is liable to be arisen when
the coated film is cured with heating after a clear coating was coated
and, therefore, this paint is not necessarily satisfactory.
SUMMARY OF THE INVENTION
The present inventors have intensively studied in order to solve the above
problems of the prior art. As a result, it has been found that the above
problems can be solved by an aqueous coating composition comprising a
specific acrylic resin and/or polyester resin, a specific polycarbonate
resin and a curing agent as a main component. Thus, the present invention
has been completed.
The main object of the present invention is to provide an aqueous coating
composition which further improves coating workability (pinhole
resistance) of the intercoating composition or aqueous metallic base
coating composition and which improves smoothness and water resistance of
the resulting coat.
This object as well as other objects and advantages of the present
invention will become apparent to those skilled in the art from the
following description.
That is, the present invention provides an aqueous coating composition
which comprises: (A) an acrylic resin and/or a polyester resin having an
acid value of 10 to 100, a hydroxyl value of 20 to 300 and a number
average-molecular weight of 1,000 to 50,000; (B) a polycarbonate resin
having a number average-molecular weight of 1,000 to 10,000 which contains
a hydroxyl group at the terminal end; and (C) a curing agent.
DETAILE DESCRIPTION OF THE INVENTION
The aqueous coating composition of the present invention is characterized
in that a specific polycarbonate resin (B) is used in an aqueous coating.
Regarding a relation among the components (A), (B) and (C), the component
(A) is a resin containing a hydrophilic group and it plays a role in being
dissolved in water or stably dispersed in water without causing layer
separation and sedimentation, and the component (C) plays a role in
subjecting to a crosslinking reaction with the resin (A) under heating
condition after coating, but stability in water and compatibility on
heating reaction of the components (A) and (C) are normally inferior.
To the contrary, the component (B) of the present invention plays an
extremely characteristic role in helping uniform water-solubilization or
water dispersion stabilization in water of the components (A) and (C) and
proceeding compatibilization during heating reaction and the following
crosslinking reaction in an uniform state.
A solubility parameter (Sp value) is used for explaining such
compatibility, and a polycarbonate resin (B) having a Sp value of 9.5 to
12.0 is preferred. Further, the solubility parameter (.delta.Sp) can be
determined by the formula:
##EQU1##
(wherein, ml is a low Sp solvent, mh is a high Sp solvent, .delta. is a
solubility parameter and V is a molecular volume in turbidity point)
described in K. W. SUH, J. M. CORBETT; Journal of Applied Polymers Science
12, 2359 (1968). This is a quantitative expression of polarity of the
substance.
That is, regarding a point which lacks any one of these components, pinhole
is liable to be arisen on curing with heating. Further, smoothness and
water resistance are not sufficient. On the other hand, the coating
composition comprising all of the components (A), (B) and (C) of the
present invention provides a coated film wherein such the defect is
improved.
The components (A) to (C) which constitute the coating composition of the
present invention will be explained in detail.
Component (A)
The acrylic resin of the component (A) is a resin having an acid value of
10 to 100, a hydroxyl value of 20 to 300 and an average-number molecular
weight of 1,000 to 50,000, which is obtained by copolymerizing an acidic
group-containing ethylenic monomer, a hydroxyl group-containing ethylenic
monomer and another ethylenic monomer. The preferred acrylic resin is a
copolymer comprising 5 to 40% by weight of an amide group-containing
ethylenic monomer, 3 to 15% by weight of an acidic group-containing
ethylenic monomer, 10 to 40% by weight of a hydroxyl group-containing
ethylenic monomer and the residual amount of an ethylenic monomer other
than the above mentioned three monomers.
Examples of the amide group-containing ethylenic monomer include
acrylamide, methacrylamide, N,N-dimethylacrylamide,
N,N-dimethylmethacrylamide, N,N-dibutylacrylamide,
N,N-dibutylmethacrylamide, N,N-dioctylacrylamide,
N,N-dioctylmethacrylamide, N-monobutylacrylamide,
N-monobutylmethacrylamide, N-monooctylacrylamide,
N-monooctylmethacrylamide and the like.
The acidic group-containing ethylenic monomer contains carboxyl group,
sulfonic group and the like. Examples of the carboxylic group-containing
monomer include styrene derivatives (e.g. 3-vinylsalicylic acid,
3-vinylacetylsalicylic acid, etc.) and (meth)acrylic acid derivatives
(e.g. acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid,
etc.). Examples of the sulfonic group-containing ethylenic monomer include
p-vinylbenzenesulfonic acid, 2-acrylamidepropanesulfonic acid and the
like.
The acidic group-containing ethylenic monomer may be half esters, half
amides and half thioesters of dibasic acid monomers. Example thereof
include half esters, half amides and half thioesters of maleic acid,
fumaric acid and itaconic acid. Examples of an alcohol which forms a half
ester include those having 1 to 12 carbon atoms, e.g. methanol, ethanol,
propanol, butanol, methyl cellosolve, ethyl cellosolve,
dimethylaminoethanol, diethylaminoethanol, acetol, allyl alcohol,
propargyl alcohol and the like. Preferred are butanol,
dimethylaminoethanol, diethylaminoethanol, acetol, allyl alcohol and
propargyl alcohol. Examples of a mercaptan which forms a half thioester
include those having 1 to 12 carbon atoms, e.g. ethylmercaptan,
propylmercaptan, butylmercaptan and the like. Examples of an amine which
forms a half amide include those having 1 to 12 carbon atoms, e.g.
ethylamine, diethylamine, butylamine, dibutylamine, cyclohexylamine,
aniline, naphthylamine and the like. Among them, the half thioester
compounds are not suitable because of their odor, and those which are
suitably used are half esters and half amides. Half-esterification,
half-thioesterification and halfamidation may be conducted at a
temperature of room temperature to 120.degree. C. in the presence or
absence of tertiary amine as a catalyst according to a normal method.
Examples of the hydroxyl group-containing ethylenic monomer include
2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl
methacrylate, 2-hydroxypropyl methacrylate,
2,4-dihydroxy-4'-vinylbenzophenone, N-(2-hydroxyethyl)acrylamide,
N-(2-hydroxyethyl)methacrylamide and the like.
The other ethylenic monomer is an ethylenic monomer containing no reactive
functional group, and examples thereof include styrenes (e.g. styrene,
.alpha.-methylstyrene, etc.), acrylates (e.g. methyl acryate, ethyl
acrylate, butyl acrylate, 2-ethylhexyl acrylate, etc.), methacrylates
(e.g. methyl methacrylate, ethyl methacrylate, butyl methacrylate,
isobutyl methacrylate, p-butyl methacrylate, etc.), nitriles (e.g.
acrylonitrile, etc.), olefins (e.g. ethylene, propylene, etc.) and the
like.
The amount of the amide group-containing ethylenic monomer is 5 to 40% by
weight, preferably 8 to 30% by weight. When the amount is smaller than 5%
by weight, the flake metal pigment is not sufficiently oriented, which
results in deterioration of appearance. On the other hand, when the amount
exceeds 40% by weight, water resistance of the resulting coat is
deteriorated. The amount of the acidic group-containing ethylenic monomer
is 3 to 15% by weight, preferably 5 to 13% by weight. When the amount is
smaller than 3% by weight, water dispersion properties become inferior. On
the other hand, when the amount exceeds 15% by weight, water resistance of
the resulting coat is deteriorated. The amount of the hydroxyl
group-containing ethylenic monomer is 10 to 40% by weight, preferably 13
to 30% by weight. When the amount is smaller than 10% by weight, curing
properties of the film become inferior. On the other hand, when the amount
exceeds 40% by weight, water resistance of the coat is deteriorated.
Further, the amount (% by weight) is based on the total weight of the
monomer.
As the polyester resin of the component (A), there can be used an oil-free
polyester resin obtained by condensing a polyhydric alcohol component with
a polybasic acid component, or an oil-modified polyester resin obtained by
reacting the polyhydric alcohol component and polybasic acid component
with an oil component as a mixture of one or more sorts of castor oil,
dehydrated castor oil, tung oil, safflower oil, soybean oil, linseed oil,
tall oil, coconut oil or a fatty acid thereof. Further, a polyester resin
obtained by grafting an acrylic resin or vinyl resin can also be used as
the component (A). Examples of the polyhydric alcohol include ethylene
glycol, diethylene glycol, propylene glycol, butanediol, pentanediol,
2,2-dimethylpropanediol, glycerine, trimethylolpropane, pentaerythritol
and the like. If necessary, a monohydric alcohol or a monoepoxy compound
containing one glycidyl group in a molecule (e.g. "CARDINILA E" (trade
name), manufactured by Shell Chemical Co., Ltd.) may be used in
combination. Examples of the polybasic acid include phthalic anhydride,
isophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic
anhydride, maleic anhydride, succinic anhydride, adipic acid, sebatic
acid, trimellitic anhydride, pyromellitic anhydride and the like. If
necessary, monobasic acids such as benzoic acid, t-butylbenzoic acid, etc.
may be used in combination.
Further, it is preferred to use an urethane-modified polyester resin as the
component (A), because it is superior in storage stability, pinhole
resistance, definition properties, tipping resistance and the like.
The component (A) above described has an acid value of 10 to 100,
preferably 30 to 80 and a hydroxyl value of 20 to 300, preferably 50 to
200. When the acid value is smaller than 10, water solubilization becomes
insufficient. On the other hand, when the acid value exceeds 100, water
resistance of the coat is deteriorated, and it is not preferred. Further,
when the hydroxyl value is smaller than 20, curing characteristics of the
coat are insufficient. On the other hand, when the hydroxyl value exceeds
300, water resistance of the coat is deteriorated, and it is not
preferred.
Further, the number-average molecular weight of the component (A) is 1,000
to 50,000, preferably 2,000 to 30,000. When the number-average molecular
weight is smaller than 1,000, hardness and water resistance of the coat
are deteriorated. On the other hand, when the number-average molecular
weight exceeds 50,000, atomization on spray coating becomes inferior,
which results in deterioration of smoothness of the coat, and it is not
preferred.
It can be easily water-solubilized by neutralizing (e.g. not less than 50%)
the carboxyl group of the component (A) with a basic substance. Examples
of the basic substance used herein include ammonia, methylamine,
ethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine,
dimethyl ethanolamine, diethanolamine, triethanolamine and the like. Among
them, diethanolamine, dimethyl ethanolamine and trimethanolamine are
preferred.
Component (B)
The component (B) is a polycarbonate resin having a number-average
molecular weight of 1,000 to 10,000, preferably 2,000 to 6,000, which
contains a hydroxyl group at the terminal end. When the number-average
molecular weight of the polycarbonate resin used in the present invention
is smaller than 1,000, pinhole resistance and water resistance of the coat
are deteriorated. On the other hand, when the number-average molecular
weight exceeds 10,000, pinhole resistance of the coat is also deteriorated
and smoothness thereof is particularly deteriorated.
The preferable polycarbonate resin is one obtained by reacting a carbonate
monomer selected from a dialkyl carbonate or an ethylene carbonate with a
straight-chain dihydric alcohol, a branched-chain dihydric alcohol and a
polyhydric alcohol having three or more hydroxyl groups, wherein the
amount of the branched-chain dihydric alcohol is at least 10 molar % based
on the total amount of the alcohol and the amount of the polyhydric
alcohol having three or more hydroxyl groups is not less than 10 molar %.
When the amount of the branched-chain dihydric alcohol is smaller than 10
molar % based on the total amount of the alcohol, the polycarbonate resin
is crystallized. On the other hand, when the amount of the polyhydric
alcohol having three or more hydroxyl groups is smaller than 10 molar %,
curing characteristics and water resistance of a coating are slightly
inferior.
Typical examples of the branched-chain dihydric alcohol include
2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, neopentyl glycol,
2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol,
2-methyl-1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol,
2-ethyl-1,3-hexanediol, 1,4-cyclohexanedimethanol, tricyclodecanemethanol
and the like.
Typical examples of the polyhydric alcohol having three or more hydroxyl
groups used in the coating composition of the present invention include
glycerine, trimethylolethane, trimethylolpropane and a dimer of
trimethylolpropane, pentaerythritol and the like.
Typical examples of the straight-chain dihydric alcohol include
1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,
1,8-octanediol, 1,9-nonanediol, 1,10-decanediol and the like.
Component (C)
The component (C) used in the coating composition of the present invention
is a curing agent (such as an amino resin and a blocked polyisocyanate).
Examples of the amino resin include di-, tri-, tetra-, penta- and
hexamethylolmelamine and alkyl etherificated products thereof (examples of
the alkyl include methyl, ethyl, propyl, isopropyl, butyl, isobutyl,
etc.), urine-formaldehyde condensates, urine-melamine condensates and the
like.
The blocked polyisocyanate is a polyisocyanate which is blocked with a
blocking agent and unblocked at an elevated temperature. Examples of the
polyisocyanates are aliphatic diisocyanates, such as trimethylene
diisocyanate, hexamethylene diisocyanate and propylene diisocyanate;
aromatic diisocyanates, such as phenylene diisocyanate and naphthalene
diisocyanate; aliphatic-aromatic diisocyanates, such as toluene
diisocyanate and tolylene diisocyanate; tri- or more polyisocyanates, such
as triphenylmethane triisocyanates, dimer or trimer of tolylene
diisocyanate; and the like. Examples of the blocking agents are alcohols,
such as methyl alcohol, ethyl alcohols; tertiary amines, such as
diethanolamine; lactams, such as caprolactam; oximes, such as methyl ethyl
ketooxime and acetone oxime; and the like.
Among them, the melamine resin is preferable and suitable examples thereof
include hydrophilic melamines and/or hydrophobic melamines, such as CYMEL
303, CYMEL 325, CYMEL 1156 (manufactured by American Cyanamide Co.); YUBAN
20N, YUBAN 20SB, YUBAN 128 (manufactured by Mitsui Toatsu Chemicals,
Inc.); SUMIMAL M-50W, SUMIMAL M-40N, SUMIMAL M-30W (manufactured by
Sumitomo Chemical Co., Ltd.) and the like. They are used alone or in
combination thereof.
The amount of the component (A) is 35 to 70% by weight, preferably 40 to
60% by weight, that of the component (B) is 5 to 50% by weight, preferably
10 to 35% by weight and that of the component (C) is 10 to 40% by weight,
preferably 20 to 30% by weight, based on the weight of the solid content
of the coating composition. When the amount of the component (A) is
smaller than 35% by weight, stability of the aqueous coating composition
is deteriorated and the viscosity of the coating composition becomes
dramatically high and, further, aggregation and sedimentation are arisen.
On the other hand, when the amount exceeds 70% by weight, curing
characteristics of the composition are deteriorated and water resistance
of the cured film is also inferior. When the amount of the component (B)
is smaller than 5% by weight, no improvement effect of the objective
coating workability (pinhole resistance and sagging resistance) is
obtained and the smoothness is inferior. On the other hand, when the
amount exceeds 50% by weight, the hardness of the coating becomes too low.
When the amount of the component (C) is smaller than 10% by weight, curing
characteristics are insufficient. On the other hand, when the amount
exceeds 40% by weight, the coating becomes too hard and it becomes
brittle.
Component (D)
The coating composition of the present invention may further contain
acrylic resin particles having a particle size of 0.01 to 1.0 .mu.m as a
component (D). The particles may be three-dimentionary crosslinked. When
the particle size is smaller than 0.01 .mu.m, the improvement effect of
workability (sagging resistance) is insufficient. On the other hand, when
the particle size exceeds 1.0 .mu.m, an appearance of the resulting
coating becomes inferior. It is preferred that the acrylic resin particles
have carboxyl groups and have an acid value of 5 or more. When the acid
value is smaller than 5, the improvement effect of workability (sagging
resistance) is insufficient. The acid value may preferably be 80 or less.
When the acid value exceeds 80, water solubility is enhanced and particle
properties are liable to be lost. Particularly preferred range of the acid
value is 10 to 70. The acrylic resin particles are preferably provided in
the form of a water dispersant.
In order to produce of the resin particles (D) containing a carboxyl group
of the present invention, a monomer (I) containing at least one carboxyl
group in a molecule is used. Examples of the monomer include styrene
derivatives (such as p-carboxyl styrene), (meth)acrylic acid derivatives,
unsaturated dibasic acids and the like, as described above. Preferred are
(meth)acrylic acid derivatives, more preferably acrylic acid, methacrylic
acid, acrylic dimer and .alpha.-hydro-.omega.-((1-oxo-2-propenyl)oxy)
poly(oxy(1-oxo-1,6-hexanediyl).
At least one sort of another monomer (II) without a carboxyl group is used,
in addition to the monomer containing at least one carboxyl group in a
molecule. This monomer is an unsaturated compound which can be radically
copolymerized with the unsaturated compound (I) having a carboxyl group.
Examples of the monomer (II) include (meth)acrylate compounds containing
no reactive functional group (e.g. methyl acrylate, methyl methacrylate,
ethyl acrylate, ethyl methacrylate, n-butyl acrylate, n-butyl
methacrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate,
2-ethylhexyl methacrylate, layryl methacrylate, phenyl acrylate, etc.),
polymerizable aromatic compounds (e.g. styrene, .alpha.-methylstyrene,
vinylketone, t-butylstyrene, parachlorostyrene, vinylnaphthalene, etc.),
hydroxyl group-containing unsaturated compounds (e.g. 2-hydroxyethyl
acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate,
hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl
methacrylate, allyl alcohol, methacryl alcohol, etc.), polymerizable amide
compounds (e.g. acrylamide, methacrylamide, N-methylolmethacrylamide,
N-methoxymethylacrylamide, etc.), polymerizable nitrile compounds (e.g.
acrylonitrile, methacrylonitrile, etc.), vinyl halide compounds (e.g.
vinyl chloride, vinyl bromide, vinyl fluoride, etc.), .alpha.-olefin
compounds (e.g. ethylene, propylene, etc.), vinyl compounds (e.g. vinyl
acetate, vinyl propionate, etc.), diene compounds (e.g. butadiene,
isoprene, etc.) and the like.
In order to synthesize three-dimensionally crosslinked resin particles, a
compound containing two or more radical-polymerizable ethylenically
unsaturated groups in a molecule can be used as the other monomer (II).
Examples thereof include polymerizable unsaturated monocarboxylic ester
compounds of polyhydric alcohol (e.g. ethylene glycol diacrylate, ethylene
glycol dimethacrylate, triethylene glycol dimethacryate, tetraethylene
glycol dimethacrylate, 1,3-butyrene glycol dimethacrylate,
trimethylolpropane triacrylate, trimethylolpropane trimethacrylate,
1,4-butanediol diacrylate, neopentyl glycol diacrylate, neopentyl glycol
dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate,
pentaerythritol diacrylate, pentaerythritol dimethacrylate,
pentaerythritol triacrylate, pentaerythritol trimethacrylate,
pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, glycerol
diacrylate, glycerol dimethacrylate, glycerol acryloxydimethacrylate,
1,1,1-trishydroxymethylethane diacrylate, 1,1,1-trishydroxymethylethane
dimethacrylate, 1,1,1-trishydroxymethylethane triacrylate,
1,1,1-trishydroxymethylethane trimethacrylate,
1,1,1-trishydroxymethylpropane diacrylate, 1,1,1-trishydroxymethylpropane
dimethacrylate, etc.), polymerizable unsaturated alcohol ester compounds
of polyhydric acid (e.g. diallyl terephthalate, diallyl phthalate,
triallyl trimellitate, etc), aromatic compounds substituted with two or
more vinyl groups (e.g. divinylbenzene, etc.), adducts of an epoxy
group-containing ethylenically unsaturated monomer and a carboxyl
group-containing ethylenically unsaturated monomer (e.g. reaction products
of glycidyl acrylate and glycidyl methacrylate with acrylic acid,
methacrylic acid, crotonic acid and maleic acid, etc.) and the like. Diene
compounds have two ethylenically unsaturated groups, which, however, act
as single polymerizable group in usual polymerization process with one
unsaturated group remaining in polymer backbone. Accordingly, the diene
compounds are classified as a monomer having one polymerizable group.
These monomers are used alone or in combination thereof.
The amount of the monomer (I) containing at least one carboxyl group in a
molecule is 1 to 50% by weight, preferably 10 to 40% by weight, and that
of the other monomer (II) is 99 to 50% by weight, preferably 90 to 60% by
weight, based on the total weight of the unsaturated compound used for
producing the water dispersant (D) of the resin particles containing a
carboxyl group.
The water dispersant (D) can be produced by emulsion-polymerizing the above
mentioned monomers (I) and (II). The emulsion polymerization is conducted
in water, if necessary, in an aqueous medium which may contain an organic
solvent such as alcohol, using a polymerization initiator.
Examples of the polymerization initiator to be used include oily azo
compounds (e.g. azobisisobutyronitrile,
2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile,
etc.), aqueous compounds (e.g. anionic 4,4'-azobis (4-cyanovaleric acid),
cationic 2,2'-azobis(2-methylpropionamidine), etc.) and the like. Examples
of the redox polymerization initiator include oily peroxides (e.g. benzoyl
peroxide, parachlorobenzoyl peroxide, lauroyl peroxide, t-butyl
perbenzoate, etc.), aqueous peroxides (e.g. potassium persulfate, ammonium
peroxide, etc.) and the like.
The reaction temperature is decided according to a kind of the initiator.
For example, the reaction temperature is 60.degree. to 90.degree. C. in
case of an azo initiator and is 30.degree. to 70.degree. C. in case of a
redox initiator. The reaction time is 1 to 8 hours. The amount of the
initiator is 0.1 to 5% by weight, preferably 0.5 to 2% by weight, based
on the total amount of the unsaturated compound.
The emulsion polymerization is fundamentally conducted by a method of
dropping the unsaturated compound. Further, it is also conducted by a
method of dropping those which are pre-emulsified using the unsaturated
compound, water and emulsifier.
As the emulsifier, there can be used those which are normally used, but
reactive emulsifiers such as RA-1022 (manufactured by Japan Emulsifier
Co., Ltd.), ELEMINOL JS-2 (manufactured by Sanyo Kasei Co., Ltd.), AQUALON
HS-10 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), etc. are
preferred. The reactive emulsifier is a surfactant having emulsifying
ability in which at least one radically polymerizable group is present,
for example an anionic, cationic or nonionic surfactant having a
(meth)acryloyl group or an allyl group.
Further, the molecular weight can be adjusted using mercaptan compounds
(e.g. lauryl mercaptan, etc.) or other compounds (e.g.
.alpha.-methylstyrene dimer, etc.) as a chain transfer agent.
The component (D) may be formulated in the amount of 3 to 70 part by
weight, preferably 5 to 55 part by weight, based on 100 parts by weight of
the solid content of the components (A) to (C). When the amount is smaller
than 3 part, no improvement effect of the coating workability (sagging
resistance) is obtained. On the other hand, when the amount exceeds 70
parts by weight, smoothness of the resulting coating is deteriorated.
Others
Further, other additives such as pigments, metal pigments, micas,
defoamers, dispersants, surface adjustors, curing catalysts (acid
catalyst), etc. may be added to the coating composition of the present
invention. It is desired for an intercoating composition that inorganic
pigments (e.g. barium sulfate, calcium carbonate, clay, titanium oxide,
etc.) are used in combination with coloring pigments in the intercoating.
The present invention relates to an aqueous coating composition comprising
water (preferably, deionized water) as a medium. However, a small amount
of organic solvents (e.g. ether alcohols such as ethylene glycol
monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol
monobutyl ether, etc.; alcohols such as methanol, ethanol, isopropano,
n-butanol, sec-butanol, t-butanol etc.; esters; ketones, etc.) may be
used, if necessary.
A metallic coating having good appearance can be obtained by a so-called
two coat/one bake coating process which comprises coating a base paint in
which a metal pigment is formulated, followed by wet-on-wet coating a
clear paint without curing the base coating, and then curing the base
coating and clear coating, simultaneously. The coating composition of the
present invention is suitable for the base paint. Examples of the clear
coating to be used in the process include melamine curing system (such as,
acryl/melamine system), acid/epoxy curing system, acryl/isocyanate curing
system, hydroxyl group/epoxy group/half ester of acid anhydride curing
system and the like.
Among them, the melamine curing system and hydroxyl group/epoxy group/half
ester of acid anhydride curing system are preferred. As the melamine
curing system, a composition comprising a melamine resin as a curing agent
and a acrylic resin containing a hydroxyl group as a main resin is
popular. The hydroxyl group/epoxy group/half ester of acid anhydride
curing system is a newly developed curing system having excellent acid
resistance and is a curing system comprising a half ester of an acid
anhydride group which is present in a polymer, a hydroxyl group and an
epoxy group, which is described in detail in Japanese Laid-Open Patent
Publication Nos. 2-45577 and 3-287650 (respectively corresponding to
Australia Patent 613,780 and U.S. Pat. No. 5,270,392 of which description
is herein incorporated).
The clear coating may also be a powder paint. As the powder paint, there
can be used a thermoplastic powder paint and thermosetting powder paint.
In view of physical properties of the coating, the thermosetting powder
paint is preferred. Examples of the thermosetting powder paint include
epoxy powder paint, acrylic powder paint and polyester powder paint. Among
them, the acrylic powder paint having good weathering resistance is
preferred. As the functional group monomer of the acrylic resin used in
the acrylic powder paint, there is a vinyl monomer containing a glycidyl
group, hydroxyl group and carboxyl group. Examples thereof include
glycidyl(meth) acrylate, methylglycidyl(meth)acrylate, hydroxyethyl
(meth)acrylate, hydroxybutyl(meth)acrylate, acrylic acid, methacrylic acid
and the like. Examples of the curing agent used in combination include
polyhydric carboxylic acid, phenol, amine, blocked isocyanate, urethodione
group-containing blocked isocyanate, alkoxyalkyl glycol, epoxy compound,
hydroxyalkylamide compound and the like. A system of epoxy-containing
acrylic resin/polyhydric carboxylic acid, which shows good appearance
because no volatile components is produced in case of curing and cause
little color change towards yellow, is preferred.
In the aqueous coating composition of the present invention, by using the
polycarbonate resin as the component (B) in combination, the concentration
of the nonvolatile content on coating becomes high and sprayablity on
spray coating becomes good. Further, since the polycarbonate resin
contains no hydrophilic group such as carboxyl group, it exhibits good
water separation (bleeding of water from the coat) and pinhole phenomenon
due to bumping of water on curing is extremely decreased, thereby
improving pinhole resistance as coating workability. In addition, the
acrylic resin particles containing the carboxyl group interact with the
amide group contained in the film-forming polymer so that the viscosity
becomes high, thereby causing no sagging even in case of the vertical
coating surface under the condition of high humidity. Further, since the
polycarbonate resin causes deterioration of the viscosity of the surface
layer of the basecoat, smoothness of the coat is improved.
As described above, according to the present invention, there is provided
an aqueous coating composition superior in coating workability (e.g.
pinhole resistance, sagging resistance, etc.) under the condition of high
humidity as well as smoothness of the coat.
EXAMPLES
The following Examples, Comparative Examples and Production Examples
further illustrate the present invention in detail but are not to be
construed to limit the scope thereof. In the Examples, Comparative
Examples and Production Examples, "part" is by weight unless otherwise
stated.
Production Example 1 (Polyester Resin)
20.51 Parts of ethylene glycol, 12.91 parts of trimethylolpropane and 51.70
parts of phthalic anhydride were mixed and the mixture was subjected to an
esterification reaction at 160.degree. to 220.degree. C. for 5 hours.
Then, 14.88 parts of trimellitic anhydride was further added to the
reaction product, which was reacted at 180.degree. C. for an hour to
obtain a polyester resin having an acid value of 50, a hydroxyl value of
60 and a number-average molecular weight of 2,000.
The polyester resin was neutralized with ethanolamine to obtain an aqueous
polyester resin varnish (I) having a neutralization degree of 80% and a
nonvolatile content of 35% by weight.
Production Example 2 (Alkyd Resin)
22.92 Parts of coconut oil fatty acid, 21.36 parts of trimethylolpropane,
14.30 parts of neopentyl glycol and 22.23 parts of phthalic anhydride were
mixed and the mixture was subjected to an esterification reaction at
160.degree. to 220.degree. C. for 5 hours. Then, 19.2 parts of trimellitic
anhydride was further added to the reaction product, which was reacted at
180.degree. C. for an hour to obtain an alkyd resin having an acid value
of 60, a hydroxyl value of 80 and a number-average molecular weight of
1,500.
The alkyd resin was neutralized with dimethylethanolamine to obtain an
aqueous alkyd resin varnish (II) having a neutralization degree of 80% and
a nonvolatile content of 35% by weight.
Production Example 3 (Acrylic Resin)
76 Parts of ethylene glycol monomethyl ether was charged into a reaction
vessel, to which was added 60 parts of a monomer mixed solution comprising
45 parts of styrene, 63 parts of methyl methacrylate, 48 parts of
2-hydroxyethyl methacrylate, 117 parts of n-butyl acrylate, 27 parts of
methacrylic acid and 3 parts of azobisisobutyronitrile, and the mixture
was heated to a temperature of 120.degree. C. with stirring. Immediately
after the temperature became 120.degree. C., 243 parts of the monomer
mixed solution was added dropwise at an uniform rate over 3 hours and then
reacted at the same temperature for an hour to obtain an acrylic resin
having an acid value of 58, a hydroxyl value of 70 and a number-average
molecular weight of 10,000.
The acrylic resin was neutralized with dimethylethanolamine to obtain an
aqueous acrylic resin varnish (III) having a neutralization degree of 80%
and a nonvolatile content of 50% by weight.
Production Example 4 (Amide Group-Containing Acrylic Resin)
76 Parts of ethylene glycol monomethyl ether was charged into a reaction
vessel, to which was added 60 parts of a monomer mixed solution comprising
15 parts of styrene, 30 parts of acrylamide, 63 parts of methyl
methacrylate, 48 parts of 2-hydroxyethyl methacrylate, 117 parts of
n-butyl acrylate, 27 parts of methacrylic acid and 3 parts of
azobisisobutyronitrile, and the mixture was heated to a temperature of
120.degree. C. with stirring. Immediately after the temperature became
120.degree. C., 243 parts of the monomer mixed solution was added dropwise
at an uniform rate over 3 hours and then reacted at the same temperature
for an hour to obtain an acrylic resin having an acid value of 58, a
hydroxyl value of 70 and a number-average molecular weight of 12,000.
The acrylic resin was neutralized with dimethylethanolamine to obtain an
aqueous acrylic resin varnish (IV) having a neutralization degree of 80%
and a nonvolatile content of 50% by weight.
Production Example 5 (Polycarbonate Resin)
To a glass reaction vessel equipped with a stirrer, a thermometer and a
fractioning column, 1000 parts of dimethyl carbonate (11.1 moles), 650
parts of 3-methyl-1,5-pentanediol (5.5 moles) and 1 part of tetraisopropyl
titanate as a catalyst were added and mixed. Then, the mixture was reacted
at 100.degree. C. for 5 hours under normal pressure and heated to
200.degree. C. over 5 hours to distill off methanol produced by the
reaction. After methanol has been completely distilled off, the reaction
was conducted for additional 2 hours under reduced pressure at 10 mmHg or
less. 99 Parts of a dimer of trimethylolpropane (0.40 moles) was added to
500 parts of the reaction product, which was reacted at 200.degree. C. for
additional 4 hours to obtain a polycarbonate resin (V) having a
number-average molecular weight of 2,350 and a hydroxyl value of 154.
Production Examples 6 to 10 (Polycarbonate Resin)
According to the same operation as that described in Production Example 5,
polycarbonate resins (VI) to (X) were obtained, using the formulations of
Table 1. The characteristics of the resulting polycarbonate resins are
shown in Table 2.
TABLE 1
__________________________________________________________________________
Produc-
tion
Example Branched-chain dihydric alcohol
Straight-chain dihydric
Polyhydric alcohol
No. Resin
DMC MPD MOD BEPD HD ND TMP D-TMP
__________________________________________________________________________
5 V 1000
650 215
(86 molar %) (14 molar %)
6 VI 1000 232 432 250
(29 molar %) (52 molar %) (19 molar %)
7 VII 1000 886 165
(82 molar %) (18 molar %)
8 VIII
1000 1000
(100 molar %)
9 IX 1000 500
(100 molar %)
10 X 1000
33 590 37
(5 molar %) (90 molar %) (5 molar
__________________________________________________________________________
%)
DMC Dimethyl carbonate
MPD 3Methylpentanediol
MOD 2Methyloctanediol
BEPD 2Butyl,2-ethylpropanediol
HD 1,6Hexanediol
ND 1,9Nonanediol
TMP Trimethylolpropane
DTMP Dimer of trimethylolpropane
TABLE 2
______________________________________
Molar % of
Produc- branched-
tion chain Molar % of
Example Molecular dihydric
polyhydric
No. Resin weight OHV alcohol alcohol
______________________________________
5 V 2350 154 86 14
6 VI 3500 100 29 19
7 VII 4750 55 83 18
8 VIII 500 220 0 0
9 IX 13000 12 0 0
10 X 2500 55 5 5
______________________________________
EXAMPLES 1 TO 6 AND COMPARATIVE EXAMPLES 1 TO 3
According to the formulation shown in Table 3, an aqueous intercoating
paint was produced. As a pigment, 80 parts of rutile titanium oxide, 20
parts of barium sulfate and 0.2 part of carbon black were formulated based
on 100 parts of the total solid content of the components (A), (B) and
(C).
These pigments were premixed with the component (A), deionized water and a
defoamer, and the premix was subjected to a dispersion treatment in a
glass beads medium for 40 minutes, using a paint conditioner.
TABLE 3
__________________________________________________________________________
Example No. Comparative Example No.
1 2 3 4 5 6 1 2 3
__________________________________________________________________________
(A) Component
Kind of resin
PE(I)
PE(I)
PE(I)
PE(I)
AL(II)
PE(I)
PE(I)
PE(I)
PE(I)
Amount 60 60 65 40 65 60 75 60 60
(B) Component
Kind of resin
PC(V)
PC(VI)
PC(VII)
PC(V)
PC(V)
PC(X)
-- PC(VIII)
PC(IX)
Amount 15 15 10 35 10 15 15 15
(C) Component
Kind of resin
C-303
C-303
C-303
C-303
C-303
C-303
C-303
C-303
C-303
Amount 25 25 25 25 25 25 25 25 25
__________________________________________________________________________
PE: Abbreviation for polyester resin
C303: Melamine resin (manufactured by Mitsui Toatsu Chemicals, Inc.)
AL: Abbreviation for alkyd resin
PC: Abbreviation for polycarbonate resin
To the resulting aqueous intercoating compositions of Examples 1 to 6 or
Comparative Examples 1 to 3, 1 part of NACURE 5225 (amine-blocked acid
catalyst, manufactured by King Industries Inc.) was added, respectively.
Thereafter, the respective mixtures were diluted with deionized water to
adjust the viscosity to 30 second/#4 Ford cup (25.degree. C.). The
intercoating solution was provided on a steel plate, on which an
electrodeposition coating had been formed in advance, by a spray coating
such that the dry film thickness became 15 to 70 .mu.m and then the coated
steel plate was baked at 150.degree. C. for 30 minutes. Thereafter, the
final surface texture of the intercoating was evaluated. The coating
conditions were adjusted to a temperature of 25.degree. C. and a humidity
of 70%.
Then, a melamine-alkyd topcoating ("ORGA G25 WHITE", manufactured by Nihon
Paint Co.) was coated on the intercoating such that the dry film thickness
became 35 to 45 .mu.m, similarly, and baked at 140.degree. for 30 minutes
to obtain a topcoating. The final surface texture and water resistance of
the top-coated steel plate were evaluated. The results are shown in Table
4.
TABLE 4
__________________________________________________________________________
Comparative
Example No. Example No.
1 2 3 4 5 6 1 2 3
__________________________________________________________________________
Pinhole critical film thickness
60<
60<
60<
60<
60<
55
30
60<
50
(.mu.m)
Sagging critical film thickness
45 45 45 45 45 45
45
30 45
(.mu.m)
Smoothness of intercoating
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.DELTA.
.smallcircle.
x
Smoothness of topcoating
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.DELTA.
.DELTA.
.DELTA.
x
Water resistance
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
x x x .smallcircle.
__________________________________________________________________________
Pinhole critical film thickness: In a coated plate having a gradient film
thickness wherein the film thickness of the thinfilm part is 15 .mu.m and
that of the thickfilm part is 70 .mu.m, the maximum film thickness at
which no coating defect (pinhole) is arisen was taken as the pinhole
critical film thickness.
Sagging critical film thickness: In a coated plate having a gradient film
thickness wherein the film thickness of the thinfilm part is 15 .mu.m and
that of the thickfilm part is 70 .mu.m, the maximum film thickness at
which no coating defect (sagging) is arisen was taken as the sagging
critical film thickness.
Coating smoothness: It was visually evaluated according to the following
criteria:
.smallcircle.: Good smoothness
.DELTA.: Smoothness is slightly inferior (round is arisen)
x: Inferior smoothness (pulled surface, orange peel surface)
Water resistance: A topcoated steel plate was dipped in hot water at
40.degree. C. for 240 hours and allowed to stand at 20.degree. C. at a
humidity of 75% for 24 hours. Then, the plate was subjected to a cross
hatch (1 mm .times. 1 mm, 100 crosses) tape peeling test to evaluate wate
resistance by the residual % of the coating.
.smallcircle.: 100/100 (No peeling)
x: 99 or less/100
EXAMPLES 7 TO 12 AND COMPARATIVE EXAMPLES 4 TO 6
According to the formulation shown in Table 5, an aqueous metallic base
paint was produced.
As a pigment, 12 parts of an aluminum pigment was formulated based on 100
parts of the total solid content of the components (A), (B) and (C). The
aluminum pigment (ALPASTE 7160N, amount of aluminum metal pigment: 65%,
manufactured by Toyo Aluminum K.K.) was uniformly premixed with the
component (C) and 2 parts of 2isostearyl acid phosphate (PHOSREX A-180L,
manufactured by Sakai Kagaku Co., Ltd.) and the resulting solution was
used as an aluminum pigment solution.
TABLE 5
__________________________________________________________________________
Example No. Comparative Example No.
7 8 9 10 11 12 4 5 6
__________________________________________________________________________
(A) Component
Kind of resin
AC(IV)
AC(IV)
AC(IV)
AC(IV)
AC(III)
AC(III)
AC(III)
AC(III)
AC(III)
Amount 60 60 65 40 65 60 755 60 60
(B) Component
Kind of resin
PC(V)
PC(VI)
PC(VII)
PC(V)
PC(V)
PC(X) -- PC(VIII)
PC(IX)
Amount 15 15 10 35 10 15 15 15
(C) Component
Kind of resin
C-303
C-303
C-303
C-303
C-303
C-303 C-303
C-303
C-303
Amount 25 25 25 25 25 25 25 25 25
__________________________________________________________________________
AC: Abbreviation for acrylic resin
C303: Melamine resin (manufactured by Mitsui Toatsu Chemicals, Inc.)
PC: Abbreviation for polycarbonate resin
Preparation of Clear Coating
90 Parts of xylene was charged into a reaction vessel and heated to
100.degree. C. A monomer mixed solution (1.2 parts of methacrylic acid,
26.4 parts of styrene, 26.4 parts of methyl methacrylate, 36.0 parts of
n-butyl acrylate, 10.0 parts of 2-hydroxyethyl acrylate and 1.0 part of
azobisisobutyronitrile) was added dropwise at an uniform rate over 3
hours, and then a solution comprising of 0.3 part of
azobisisobutyronitrile and 10.0 parts of xylene was added dropwise over 30
minutes. The reaction was continued for additional 2 hours to obtain an
acrylic resin solution having a nonvolatile content of 50% and a
number-average molecular weight of 8,000.
By using the acrylic resin, a clear coating was prepared according to the
following formulation.
______________________________________
Formulation of clear coating
______________________________________
Acrylic resin solution 100 Parts
YUBAN 20SE-60 36 Parts
(manufactured by Mitsui Toatsu Chemicals, Inc.)
MODAFLOW 0.5 Part
(manufactured by Monsanto Co.)
______________________________________
To the resulting aqueous metallic base coating compositions of Examples 7
to 12 or Comparative Examples 4 to 6, 1 part of NACURE 5225 (amine-blocked
acid catalyst, manufactured by King Industries Inc.) was added,
respectively. Thereafter, the respective mixtures were diluted with
deionized water to adjust the viscosity to 30 second/#4 Ford cup
(25.degree. C.). The solution was coated on a steel plate, on which an
intercoating had been provided in advance, by a spray coating such that
the dry film thickness became 15 to 50 .mu.m and then dried at 80.degree.
C. for 2 minutes. Thereafter, a clear paint was coated such that the dry
film thickness became 30 .mu.m and set for 7 minutes, and then baked at
140.degree. C. for 30 minutes. Thereafter, the final surface texture and
water resistance of the coating were evaluated. The results are shown in
Table 6. The coating conditions were adjusted to a temperature of
25.degree. C. and a humidity of 70%.
TABLE 6
______________________________________
Comparative
Example No. Example No.
7 8 9 10 11 12 4 5 6
______________________________________
Pinhole critical film
35 35 35 35 35 30 20 30 20
thickness (.mu.m)
Sagging critical film
30 30 25 30 30 25 20 10 25
thickness (.mu.m)
Smoothness of coating
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.DELTA.
.DELTA.
x
Appearance of coating
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.DELTA.
x x x
(flip effect)
Water resistance
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
x x x .smallcircle.
______________________________________
Appearance of coating:
.smallcircle.: Good (orientation of aluminum is good, and a flopped value
measured by a metallic aviarance tester is not less than 30)
.DELTA.: Slightly inferior (orientation of aluminum is slightly inferior,
and a flopped value is within a range of 25 to 30)
x: Inferior (orientation of aluminum is inferior, and a flopped value is
less than 25)
Production Example 11 (Emulsion-Polymerized Particles)
185 Parts of deionized water was charged into a 500 ml vessel equipped with
a nitrogen introducing tube, a stirrer, a cooler, a thermal regulator and
a dropping funnel, and heated to 83.degree. C. A mixture comprising 20
parts of ALONIX M5300 (manufactured by Toagosei Chemical Industry Co.,
Ltd.), 5.9 parts of dimethylethanolamine and 80 parts of styrene was added
dropwise from the dropping funnel over 2 hours. At the same time, a
solution as an initiator prepared by neutralizing 1 part of
4,4'-azobis-4-cyanovaleric acid with 0.55 part of dimethylethanolamine,
followed by dissolving in 40 parts of deionized water was added dropwise.
The mixture was stirred at 83.degree. C. for additional one hour and then
cooled to obtain a milk white emulsion (XI) having a solid content of 30%
and a particle size of 100 nm (laser light scattering method).
Production Example 12 (Emulsion-Polymerized Particles)
According to the same operation as that described in Production Example 9
except that the amount of deionized water on initial charging was 197
parts and 5.6 parts of a reactive emulsifier RA-1022 (manufactured by
Nippon Emulsifier Co., Ltd.) was added to the monomer mixture, a milk
white emulsion (XII) having a solid content of 30% and a particle size of
94 nm (laser light scattering method) was obtained.
Production Example 13 (Emulsion-Polymerized Particles)
180 Parts of deionized water, 10 parts of styrene, 0.7 part of methacrylic
acid and 0.7 part of dimethylethanolamine were charged into the same
reaction vessel as that of Production Example 9 and heated to 83.degree.
C. Then, a solution prepared by neutralizing 0.5 part of
4,4'-azobis-4-cyanovaleric acid with 0.27 part of dimethylethanolamine,
followed by dissolving in 5 parts of deionized water was added dropwise
over 20 minutes. Further, a mixture comprising 84.3 parts of styrene, 5
parts of methacrylic acid and 5 parts of dimethylethanolamine and a
solution prepared by neutralizing 0.5 part of 4,4'-azobis-4-cyanovaleric
acid with 0.27 part of dimethylethanolamine, followed by dissolving in 40
parts of deionized water were added dropwise over 2 hours. The mixture was
stirred for additional one hour to obtain a milk white emulsion (XIII)
having a solid content of 30% and a particle size of 330 nm (laser light
scattering method).
Production Example 14 (Polyester Resin)
A reaction vessel was charged with 9.30 parts of ethylene glycol, 28.80
parts of 2-butyl-2-ethyl-1,3-propane diol, 12.91 parts of
trimethylolpropane, 40.55 parts of isophtharic acid and 16.12 parts of
hexahydrophtharic anhydride, and heated at a temperature of 160.degree. to
220.degree. C. to esterify for 7 hours. To the content, 13.39 parts of
trimellitic anhydride was added and reacted at 180.degree. C. for one hour
to obtain a polyester resin having an acid value of 45, a hydroxyl value
of 70 and a number average molecular weight of 2,500.
The resulting resin was neutralized with diethanolamine to obtain an
aqueous polyester resin varnish (XIV) having a neutralizing degree of 80%
and a nonvolatile content of 35% by weight.
Production Example 15 (Crosslinked Particles)
A milk white emulsion (XV) having a solid content of 30% and a particle
size of 91 nm (laser light scattering method) was obtained as generally
described in Production Example 11, with the exception that 70 parts of
styrene and 10 parts of ethyleneglycol dimethacrylate were employed
instead of 80 part of styrene.
EXAMPLES i TO ix AND COMPARATIVE EXAMPLES i TO v
According to the formulation shown in Table 7, an aqueous metallic base
paint was prepared.
As a pigment, 12 parts of an aluminum pigment was formulated for 100 parts
of the total solid content of the components (A), (B) and (C) and the
emulsion-polymerized particles (D). The aluminum pigment (ALPASTE 7160N,
amount of aluminum metal pigment: 65%, manufactured by Toyo Aluminum K.K.)
was uniformly premixed with melamine resin and 2 parts of isostearyl acid
phosphate (PHOSREX A-180L, manufactured by Sakai Kagaku Co., Ltd.) and the
resulting solution was used as an aluminum pigment solution.
TABLE 7
__________________________________________________________________________
Example No.
i ii iii iv v vi vii
__________________________________________________________________________
(A) Kind of
AC(IV)
AC(IV)
AC(IV)
AC(IV)
AC(IV)
PE(XIV)
PE(XIV)
Component
resin
Amount
45 45 55 35 35 45 45
(B) Kind of
PC(V) PC(VI)
PC(VII)
PC(X)
PC(V)
PC(V)
PC(V)
Component
resin
Amount
15 15 10 35 5 15 15
(C) Kind of
C-303 C-303
C-303
C-303
C-303
C-303
C-303
Component
resin
Amount
25 25 25 25 25 25 25
(D) Kind of
EM(XI)
EM(XII)
EM(XI)
EM(XI)
EM(XI)
EM(IX)
--
Component
resin
Amount
15 15 10 5 35 15
__________________________________________________________________________
Example No.
Comparative Example No.
viii ix i ii iii iv v
__________________________________________________________________________
(A) Kind of
AC(IV)30
AC(IV)
AC(IV)
AC(IV)
AC(IV)
AC(IV)
AC(III)
Component
resin
Amount
PE(XIV)15
45 50 50 45 45 45
(B) Kind of
PC(V) PC(V)
-- PC(V)
PC(VIII)
PC(IX)
PC(V)
Component
resin
Amount
20 15 25 15 15 15
(C) Kind of
C-303 C-303
C-303
C-303
C-303
C-303
C-303
Component
resin
Amount
25 25 25 25 25 25 25
(D) Kind of
EM(X) EM(XV)
EM(XI)
-- EM(XI)
EM(XI)
EM(XI)
Component
resin
Amount
10 15 25 15 15 15
__________________________________________________________________________
AC: Acrylic resin
PE: Polyester resin
PC: Polycarbonate
C303: Melamine resin
EM: Emulsion polymerized particles
Preparation of Clear Paint (1)
90 Parts of xylene was charged into a reaction vessel and heated to
100.degree. C. A monomer mixed solution (1.2 parts of methacrylic acid,
26.4 parts of styrene, 26.4 parts of methyl methacrylate, 36.0 parts of
n-butyl 0.3 part of azobisisobutyronitrile and 10.0 parts of xylene was
added dropwise over 30 minutes. The reaction was continued for additional
2 hours to obtain an acrylic resin solution having a nonvolatile content
of 50% and a number-average molecular weight of 8,000.
By using this acrylic resin, a clear paint (1) was prepared according to
the following formulation.
______________________________________
Formulation of clear paint (1)
______________________________________
Acrylic resin solution 100 Parts
YUBAN 20SE-60 36 Parts
(manufactured by Mitsui Toatsu Co., Ltd.)
MODAFLOW 0.5 Part
(manufactured by Monsanto Co.)
______________________________________
To the resulting aqueous metallic base paints of Examples i to viii and
Comparative Examples i to v, 1 part of NACURE 5225 (amine-blocked acid
catalyst, manufactured by King Industries Inc.) was added, respectively.
Thereafter, the respective mixtures were diluted with deionized water to
adjust the viscosity to 30 second/#4 Ford cup (25.degree. C.). The
solution was coated on a steel plate, on which an intercoating had been
provided in advance, by spray coating such that the dry film thickness
became 10 to 50 .mu.m and then dried at 80.degree. C. for 2 minutes.
Thereafter, a clear paint (1) was coated such that the dry film thickness
became 30 .mu.m and set for 7 minutes, and then baked at 140.degree. C.
for 30 minutes. Thereafter, the final surface texture and water resistance
of the coating were evaluated. The results are shown in Table 8. The
coating conditions were adjusted to a temperature of 25.degree. C. and a
humidity of 70% and
TABLE 8
______________________________________
Example No.
i ii iii iv v vi vii viii ix
______________________________________
Humid-
Pinhole critical
40 40 40 40 35 40 40 40 40
ity film thickness
of 70%
(.mu.m)
Sagging critical
40 40 40 35 40 35 35 40 40
film thickness
(.mu.m)
Smoothness of
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
coating
Appearance of
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
coating (flip
effect)
Water resist-
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
ance of coat
Humid-
Pinhole critical
35 35 35 35 30 35 35 35 35
ity film thickness
of 85%
(.mu.m)
Sagging critical
35 35 30 30 35 30 30 35 38
film thickness
(.mu.m)
Smoothness of
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
coating
Appearance of
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
coating (flip
effect)
______________________________________
Comparative Example No.
i ii iii iv v
______________________________________
Humid-
Pinhole critical
15 30 15 20 15
ity film thickness
of 70%
(.mu.m)
Sagging critical
25 10 10 25 15
film thickness
(.mu.m)
Smoothness of
x .smallcircle.
.DELTA.
x .DELTA.
coating
Appearance of
.DELTA.
x x .DELTA.
x
coating (flip
effect)
Water resist-
x .smallcircle.
x .smallcircle.
x
ance of coating
Humid-
Pinhole critical
10> 20 10 10 10
ity film thickness
of 85%
(.mu.m)
Sagging critical
20 10> 10> 10> 10>
film thickness
(.mu.m)
Smoothness of
x .smallcircle.
x .DELTA.
.DELTA.
coating
Appearance of
x x x .DELTA.
x
coating (flip
effect)
______________________________________
EXAMPLE A
The aqueous metallic coating compositions obtained in Examples i to viii
were diluted with deionized water to adjust the viscosity to 30 second/#4
Ford cup (25.degree. C.). The solution was coated on a steel plate, on
which an intercoating had been provided in advance, by spray coating such
that the dry film thickness became 10 to 50 .mu.m and then dried at
80.degree. C. for 2 minutes. Thereafter, a clear coating (2) was coated
such that the dry film thickness became 30 .mu.m and set for 7 minutes,
and then baked at 140.degree. C. for 30 minutes. Thereafter, the final
surface texture and water resistance of the coating were evaluated. The
results are shown in Table 9. The coating conditions were adjusted to a
temperature of 25.degree. C. and a humidity of 70% and 85%.
TABLE 9
______________________________________
Example No.
Base coating to be used
i ii iii iv v vi vii viii
______________________________________
Humid- Pinhole critical
40 40 40 40 35 40 35 40
ity film thickness
of 70% (.mu.m)
Sagging critical
40 35 40 30 40 35 30 40
film thickness
(.mu.m)
Smoothness of
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
coating
Appearance of
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
coating (flip
effect)
Water resist-
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
ance of coating
Humid- Pinhole critical
35 35 35 35 30 35 30 35
ity film thickness
of 85% (.mu.m)
Sagging critical
35 35 30 30 35 30 25 35
film thickness
(.mu.m)
Smoothness of
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
coating
Appearance of
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
coating (flip
effect)
______________________________________
Preparation of Clear Coating (2)
(1) Production of varnish
500 Parts of butyl acetate was charged into a 2 liter reaction vessel
equipped with a nitrogen introducing tube, a stirrer, a condenser, a
thermal regulator and a dropping funnel, and heated to 125.degree. C. A
solution comprising 50 parts of styrene, 400 parts of glycidyl
methacrylate, 350 parts of 2-hydroxyethyl methacrylate, 200 parts of
2-ethylhexyl acrylate and 70 parts of t-butylperoxy- 2-ethyl hexanoate was
added dropwise from the dropping funnel over 3 hours. After the completion
of the addition, the mixture was maintained at 125.degree. C. for 30
minutes. Then, a solution comprising 10 parts of t-butylperoxy-2-ethyl
hexanoate and 250 parts of xylene was added dropwise over 30 minutes.
After the completion of the addition, the reaction was continued at
125.degree. C. for additional 2 hours to obtain an acrylic resin varnish
having a nonvolatile content of 59% and a number-average molecular weight
of 4,000.
(2) Production of carboxylic anhydride group-containing polymer
80 Parts of xylene was charged into a 1 liter reaction vessel equipped with
a nitrogen introducing tube, a stirrer, a condenser, a thermal regulator
and a dropping funnel, and heated to 115.degree. C. A monomer comprising
25 parts of styrene, 21 parts of N-butyl acrylate, 95 parts of N-butyl
methacrylate, 34 parts of 2-ethylhexyl methacrylate, 50 parts of itaconic
anhydride, 100 parts of propylene glycol monomethyl ether acetate and 10
parts of t-butylperoxy-2-ethyl hexanoate and an initiator solution were
added dropwise over 3 hours. Further, the mixture was stirred for
additional 2 hours to obtain a carboxylic anhydride group-containing
polymer having a nonvolatile content of 53% and a number-average molecular
weight of 5,500.
(3) Production of half-esterified polymer
To 385 parts of the carboxylic anhydride group-containing polymer
synthesized in the above item (2), 1.35 parts of triethylamine dissolved
in 35 parts of butyl acetate and 18.2 parts of methanol were added, and
the mixture was reacted at 40.degree. C. for 12 hours to confirm by IR
that absorption of the acid anhydride group (1785 cm.sup.-1) has been
completely disappeared. Thus, a half-esterified polymer was obtained.
(4) Production of Clear Paint
100 Parts of the varnish produced in the above item (1), 133.0 parts of the
carboxylic anhydride group-containing polymer produced in the above item
(3), 0.3 part of tetrabutylammonium bromide, 1.2 parts of TINUVIN-900
(benzotriazole UV absorber, manufactured by Ciba Geigy Co.) and 0.6 part
of SANOL LS-292 (hindered amine photostabilizer, manufactured by Mitsui
Co., Ltd.) were charged into a stainless vessel and the mixture was
stirred by a laboratory stirrer to produce a clear paint. This clear paint
was diluted with thinner (butyl acetate/xylene =1/1) to give a clear paint
having a coating viscosity.
EXAMPLE B
To the resulting aqueous metallic base paints of Examples i to v and
Comparative Examples i to viii, 1 part of NACURE 5225 (amine-blocked acid
catalyst, manufactured by King Industries Inc.) was added, respectively.
Thereafter, the respective mixtures were diluted with deionized water to
adjust the viscosity to 30 second/#4 Ford cup (25.degree. C.). The
solution was coated on a steel plate, on which an intercoating had been
provided in advance, by spray coating such that the dry film thickness
became 10 to 50 .mu.m and then dried with heating at 80.degree. C. for 2
minutes. Thereafter, a powder coating was coated such that the dry film
thickness became 80 .mu.m and then baked at 160.degree. C. for 30 minutes.
Thereafter, the final surface texture and water resistance of the coat
were evaluated. The results are shown in Table 10. The coating conditions
were adjusted to a temperature of 25.degree. C. and a humidity of 70% and
85%.
TABLE 10
__________________________________________________________________________
Example No. Comparative Example No.
Base coating to be used
i ii
iii
iv
v vi
vii
viii
i ii iii iv v
__________________________________________________________________________
Humidity
Pinhole critical
40
40
40
40
35
35
35
35 15 30 15 20 15
of 70%
film thickness (.mu.m)
Sagging critical
40
40
40
30
40
35
30
35 25 10 10 25 15
film thickness (.mu.m)
Smoothness of
.DELTA.
.DELTA.
.DELTA.
.DELTA.
.DELTA.
.DELTA.
.DELTA.
.DELTA.
x .DELTA.
x x x
coating
Appearance of
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.DELTA.
x x .DELTA.
x
coating (flip
effect)
Water resistance
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
x .smallcircle.
x .smallcircle.
x
of coating
Humidity
Pinhole critical
35
35
35
35
30
35
35
35 10>
20 10 10 10
of 85%
film thickness (.mu.m)
Sagging critical
35
35
30
30
35
30
25
35 20 10>
10>
10>
10>
film thickness (.mu.m)
Smoothness of
.DELTA.
.DELTA.
.DELTA.
.DELTA.
.DELTA.
.DELTA.
.DELTA.
.DELTA.
x .DELTA.
x x x
coating
Appearance of
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
x x x .DELTA.
x
coating (flip
effect)
__________________________________________________________________________
In Table 10, "smoothness" was determined by the relative evaluation in case
that the powder clear is used only.
Production Example of Resin for Powder Paint
63 Parts of xylene was charged into a flask equipped with a dropping
funnel, an agitating element and a thermometer and heated to 130.degree.
C. A solution comprising 20 parts of styrene, 27 parts of methyl
methacrylate, 45 parts of glycidyl methacrylate, 8 parts of isobutyl
methacrylate and 7.5 parts of t-butylperoxy-2-ethyl hexanoate was added
dropwise to the flask at an uniform rate over 3 hours, using the dropping
funnel. After the completion of the addition, the mixture was maintained
for 30 minutes. Then, 7 parts of xylene and 0.1 part of
t-butylperoxy-2-ethyl hexanoate were added dropwise at an uniform rate,
using the dropping funnel. After the completion of the addition, the
mixture was maintained at 130.degree. C. for additional one hour. Then,
xylene was distilled off under reduced pressure to obtain an acrylic
resin.
70 parts of the resulting acrylic resin, 19.1 parts of decanedicarboxylic
acid, 0.11 part of CF-1056 and 0.89 part of benzoin were dry-mixed by a
Henschel mixer (manufactured by Mitsui Miike Seisakusho Co., Ltd.) and
then dissolved/dispersed at 100.degree. C. by a CONEADER PR-46
(manufactured by Buss Co. Switzerland). After cooling, it was pulverized
by a hammer mill and classified through a 150 mesh woven metal to obtain
an acrylic powder clear paint.
Coating Process of Acrylic Powder Paint
It was conducted by an electrostatic coating method.
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